A:Answer TL;DR, Yes, it’s normal, annoying, but normal.
The “I have a lot of time on my hands” version: I believe this is normal. Due to how speed is managed on these kinds of motors. Without getting to technical, it just varies the amount of power it sends to the motor depending on the desired speed. And since AC power is inherently inconsistent (Alternating Current), it means that if the fan is not running at full boar, you’re going to hear it go in and out a bit. While companies do make DC motors that minimize this issue, those tend to be much more expensive, and require more advanced power management to convert AC wall power the DC voltage. So it really stinks, but unless you want to pay 1-2x the cost of this fan, it’s a suckage we must endure :(
